CircRNAs have been reported to exert momentous roles in regulating pathophysiological process and guiding clinical diagnosis and treatment in colorectal cancer (CRC). However, there are still a lot of circRNAs that need to be unearthed. In this study, we evaluated the expression profile of circRNAs in 10 CRC tissues and their corresponding normal-appearing tissues (NATs) by microarray, and identified that hsa_circ_101555 (circ101555) was significantly up-regulated in tumor tissues and closely related to the prognosis of CRC patients. A specific close loop structure of circ101555 was described, which was generated by back-splicing of the host gene CSNK1G1 and showed greater stability than the linear RNA. The results in vitro and in vivo showed that silencing circ101555 expression significantly suppressed cell proliferation, induced apoptosis and impaired the DNA repair capacity of CRC cells, while rescue experiments suggested that down-expression of miR-597-5p could significantly attenuate the biological effects of circ101555 knockdown on CRC cells. Subsequent experiments in vitro, including double fluorescence in situ hybridization (D-FISH) analysis, RIP analysis and biotin-coupled probe pull down assay, confirmed that miR-597-5p was effectively enriched by circ101555, and circ101555 might serve as a sponge of miR-597-5p. Moreover, two putative oncogenes (CDK6 and RPA3) were identified as the miR-597-5p potential targets. Taken together, our results proved that circ101555 might function as a competing endogenous RNA of miR-597-5p to up-regulate CDK6 and RPA3 expression in CRC. Circ101555 could be a useful prognostic indicator in patients with CRC, and silence of circ101555 provided a new attractive therapeutic measure for CRC.